Earlier, a support page from Microsoft stated that the Windows 10 Mobile Insider Preview would be expiring on October 1, 2015 leading many to believe that the company would be ending the Preview then, as it moved to focus on the RTM date.
However, Microsoft"s Gabe Aul has now clarified the statement, saying that the date specifies when the certificate for the current Insider build expires. According to Aul, the Preview will continue, however it will be using a new certificate. In short, the Windows 10 Mobile Insider Preview will continue even after this date.
@Mkeallison That"s just date when the cert currently used to sign builds expires. The program will continue. New builds will use new cert.
— Gabriel Aul (@GabeAul) August 27, 2015